A variety of methods are available for the manufacture of 2-perfluoroalkylethyl alcohols from 2-perfluoroalkylethyl iodides. Some methods suffer the disadvantages of using metallic catalysts and/or organic solvents, neither of which can be allowed to escape into the environment (U.S. Pat. No. 4,748,282, U.S. Pat. No. 478,760, U.S. Pat. No. 4,452,852, U.S. Pat. No. 4,001,309, U.S. Pat. No. 4,219,681 and DE 3016571). Others require the use of either expensive percarboxylic acids (U.S. Pat. No. 4,613,681) or refrigeration (DT 2628705). Still others afford only partial conversions or products of low purity (DT 18677, EP 245133A, J 55009025 and J 50047912).
While the method described by Day in U.S. Pat. No. 3,283,012, for the conversion of 2-perfluoroalkylethyl iodides to 2-perfluoroalkylethyl alcohols, does not suffer from the disadvantages cited above, it still is not without disadvantages of its own. Two main chemical reactions, sulfation and hydrolysis, take place in the manufacture of 2-perfluoroalkylethyl alcohols as described by Day. In the first, 2-perfluoroalkylethyl iodides are converted to 2-perfluoroalkylethyl pyrosulfates (described by Day as sulfates) by treatment with oleum. In the second, hydrolysis of the pyrosulfates results in the formation of the sulfates which, in turn, are converted to the desired 2-perfluoroalkylethyl alcohols. It is believed that, in the first step, an intermediate unstable sulfonyl iodide is formed which is then converted either to an alkyl pyrosulfate if contacted by additional sulfur trioxide, or to a bis-sulfate if no additional sulfur trioxide is immediately available. For this reason, an excess of oleum is used to mininize the formation of the bis sulfate which is undesirable because its rate of hydrolysis is much slower than that of the sulfate thus tending to increase its level, as well as the level of other impurities derived from it, in the product. No matter which reaction takes place, the main by-products of the reaction are elemental iodine and sulfur dioxide which react with water during the hydrolysis, to produce hydrogen iodide and sulfuric acid. The following is a representation, not intended to be limiting, of the various reactions (wherein R=RfCH.sub.2 CH.sub.2); ##STR1##
When the first of the above reactions is carried out according to the procedures of Day, molten iodide is added to 65% oleum at 50.degree.-55.degree. C. over the course of 5-6 hours at atmospheric pressure. The reaction is vigorously exothermic. The temperature of the mass is controlled at 50.degree.-55.degree. C. during the addition to maintain most of the iodides as liquids, ready to react, thus preventing the build-up of solidified unreacted iodide which could lead to an uncontrollable condition, if, for some reason, all were to melt at one time and become available for reaction. During the addition of the molten iodide to the oleum, severe foaming occurs due to the viscous nature of the mass, the vigorously exothermic reaction, the formation of low-boiling by-product sulfur dioxide and the closeness of the reaction temperature to the boiling point of the sulfur trioxide in the oleum. The foaming, in turn, reduces the efficiency of the agitation leading to localized higher temperatures and deficencies in excess sulfur trioxide, both of which conditions favor increased undesirable bis sulfate formation. The foaming also reduces heat transfer efficency resulting in prolonged processing. Purer intermediate 2-perfluoroalkylethyl pyrosulfate would be obtained if the foaming could be avoided.
When the second main reaction, i.e., the hydrolysis, is carried out according to the methods of Day, the viscous sulfation mass, containing about 30-38% free sulfur trioxide, is added to water at atmospheric pressure with cooling. The reaction is so exothermic that it is violent. Splattering occurs at the surface, carrying insoluble materials into the scrubber. This condition is compounded by the formation of 2-perfluoroalkylethyl hydrate gels which form at the higher temperatures of the drowning. The gels rise in the mass, thereby reducing agitation at the surface and causing localized hot spots which lead to more severe splattering. The reduced agitation also results in intermittent thermal shocks which, in turn, have a deleterious effect on the glass-lined equipment. Vent losses and equipment failures could be avoided or minimized if a more controllable process were developed.
The problems associated with the sulfation and hydrolysis steps, were avoided in part by carrying out both reactions under pressure. Vent losses were reduced in both cases, but violent surface reactions were still experienced, especially in the case of the hydrolysis. In addition, serious safety concerns arose in connection with operating under pressure with large of quantities of such highly reactive chemicals.